Apparatus and method for monitoring a state, in particular of a fuse

ABSTRACT

The present invention provides an apparatus for monitoring a state, in particular of a fuse ( 4 ), having: a first state storage device ( 11 ) for storing a state, in particular of a fuse ( 4 ); a second state storage device ( 12 ) for storing the state of the first state storage device ( 11 ); and a logic device ( 9 ) for comparing the states of the two state stores ( 11, 12 ); the first state store ( 11 ) being able to be driven for renewed reading in of the state, in particular of the fuse ( 4 ), in the event of a noncorrespondence of the states in the two stores ( 11, 12 ). The present invention likewise provides a method for monitoring a state, in particular of a fuse.

[0001] The present invention relates to an apparatus and a method formonitoring a state, in particular of a fuse.

[0002] Latching fuse state storage circuits (fuse latch circuits) areused to store apparatus-relevant information, such as e.g. the state ofa fuse, or repair information for memory chips. Latching fuse statestores (fuse latches) are exposed to the influence of errors that can berectified, to a disturbance mechanism which is caused by particles, inparticular α particles, which penetrate through the active state storagearea and alter the state of the state store.

[0003] This represents a serious problem since the apparatus may be inoperation for an indeterminate length of time and the error (incorrectstored state of the fuse to be monitored) is not corrected since thestate stores (latches) are only set during the run-up or during thestart of the apparatus. Module-relevant information, such as the repairinformation, is lost and cannot be recovered while the apparatus isactive. Even more important is the fact that errors which [lacuna] bysuch state stores (latches) that have changed over unintentionally aredifficult to detect. In present-day designs, the setting of the statestore (set a fuse latch) is a “global” operation, which means that allthe state stores (fuse latches) are set simultaneously. Therefore, it isnot possible to refresh the state store information while the apparatusis active.

[0004] The problem has been alleviated hitherto by derating a statestorage circuit (fuse latch circuit). This reduces the probability of anerror occurring, but ultimately does not solve the problem.

[0005]FIG. 1 illustrates a customary state storage circuit. A supplyvoltage 1 (VDD) is connected via a first switching device 23, inparticular a field-effect transistor, to an actual state store 3 (fuselatch), which has two inverters I. The first switching device 23 isactuated by a first drive signal 5 (FPUP). Via a connection 16, thefirst switching device 23 is connected to a second switching device 24,which is actuated by a second drive signal 6 (FPUN). Located between thesecond switching device 24 and a ground terminal 2 is the fuse 4 whosestate is monitored by the circuit in accordance with FIG. 1. In parallelwith the connection 16 between the first switching device 23 and thesecond switching device 24, the two inverters I are connected in series,between the two inverters a signal branching off to a detection device15, in particular a decoding device.

[0006]FIG. 2 shows the drive signals 5, 6 plotted against time in orderto elucidate the method of operation of the arrangement according toFIG. 1. The drive signal 5 (FPUP), which is applied to the firstswitching device 23, controls the resetting (reset) of the state store3. After the run-up, a low level signal at the switching device 23effects a resetting 7 (reset) of the state store 3 (latch). The seconddrive signal 6 (FPUN) controls the setting (set) of the state store 3(latch), in which case, in the event of a high level signal at thesecond switching device 24, the state store 3 (latch) is set 8 (setlatch) in accordance with the state of the fuse 4, which may be intactor blown. This operation is effected only once in each case after theactivation of the apparatus during the run-up sequence in the event of astart-up.

[0007] It is an object of the present invention to provide an apparatusand a method for monitoring the state of a fuse which identifies, and inparticular corrects, state storage devices (fuse latch) that haveswitched over unintentionally, without impeding the operation of theapparatus during the monitoring process.

[0008] According to the invention, this object is achieved by means ofthe apparatus specified in claim 1 and by means of the method accordingto claim 8.

[0009] The idea underlying the present invention consists in providing asecond state storage device (e.g. fuse latch) and a statecomparison/control logic.

[0010] In the present invention, the problem mentioned in theintroduction is solved in particular by the states of two state storagedevices (e.g. fuse latches) being compared in a comparison/control logicand, in the event of a noncorrespondence of the two states, a renewedchecking of the state, e.g. of the fuse, being carried out withsubsequent copying of the state acquired in the first state storagedevice into the second state storage device.

[0011] Advantageous developments and improvements of the respectivesubject matter of the invention are found in the subclaims.

[0012] In accordance with one preferred development, the first statestore can be driven for reading in the state, in particular of the fuse,by the logic device.

[0013] In accordance with a further preferred development, the apparatushas a switching device, which can be driven by a copying signal forcopying the state stored in the first storage device into the secondstorage device by the logic device.

[0014] In accordance with a further preferred development, the logicdevice can generate an error signal for indicating the noncorrespondenceof the two states in the two storage devices.

[0015] In accordance with a further preferred development, the secondstate store is connected to one or more decoding devices.

[0016] In accordance with a further preferred development, the apparatusis used in a semiconductor memory device.

Exemplary embodiments of the invention are illustrated in the drawingsand are explained in more detail in the description below. In thefigures:

[0017]FIG. 1 shows the circuit diagram of a customary state storagecircuit (fuse latch circuit);

[0018]FIG. 2 shows the signal waveform of two drive signals forelucidating the method of operation of the arrangement according to FIG.1; and

[0019]FIG. 3 shows the block diagram of an apparatus for elucidating anembodiment of the present invention.

[0020] In the figures, identical reference symbols designate identicalor functionally identical constituent parts.

[0021]FIG. 3 shows the block diagram of an apparatus for monitoring thestate of a fuse for elucidating an embodiment of the present invention.

[0022]FIG. 3 illustrates a first state storage device 11, which isconnected to a ground terminal 2 (GND) via a fuse 4. A first drivesignal 5 (FPUP) and a second drive signal 6 (FPUN) are applied to thefirst state storage device 11. Via a connection 21, the first statestorage device 11 is connected to a logic device 9, which performs inparticular comparison and control tasks (compare/control logic). Asecond state storage device 12 is likewise connected to the logic device9 via a connection 22.

[0023] Located between the first state storage device 11 and the secondstate storage device 12 is a switching device 14, which is actuatedaccording to the logic device 9. The first state storage device 11(first fuse latch) essentially corresponds to the customary statestorage device explained with reference to FIG. 1 and is used to detectthe state of the fuse 4. However, instead of being connected directly toa decoding device 15 or a decoding circuit, as shown in FIG. 1, thefirst state storage device 11 can be connected to the second statestorage device according to the switching device 14, the second statestorage device (second fuse latch) being connected to the decodingdevice 15.

[0024] The switching device 14 allows the copying of the state stored inthe first state storage device 11 into the second state storage device12. The logic device 9 compares, in particular permanently, the contentsof the two state storage devices 11, 12 and, in the case of a detectednoncorrespondence of the two states in the state storage devices 11, 12,can cause, via the connections 25, 26, which, in particular, transmitsignals whose signal waveform corresponds to that of the first and/orsecond drive signal 5, 6, the first state storage device 11 to check thestate of the fuse 4 anew and to forward the newly generated storagecontent of the first state store 11 via the switching device 14 to thesecond state storage device 12 according to a copying signal 10, whichissues from the logic device 9 to the switching device 14.

[0025] An error signal 13 (error) can be communicated to other circuitsections or systems (not illustrated) by the logic device 9. Such adisturbance, in particular the noncorrespondence of the two states whichare stored in the two state storage devices 11, 12, occur [sic] as aresult of the impinging of particles on the state storage areas, inparticular as a result of the impinging of α particles.

[0026] According to the present invention, the state of the first statestorage device 11 can be adjusted anew with the state of the fuse 4 tobe monitored, without being superimposed with the operation of theapparatus, and can consequently serve as a reference. In the case of adetected noncorrespondence of the states of the two state storagedevices 11, 12, it is initially not known whether the first or secondstate storage device 10 or 11 has an item of information that iscorrupted, in particular by an α particle.

[0027] The detection of a noncorrespondence initiates a renewed checkingof the state of the fuse 4 and a renewed storage of said state in thefirst state storage device 11, which is followed by a process of copyingto the second state storage device 12. This process can take placelocally and only for the state storage devices 11, 12 (fuse latches)which exhibit a noncorrespondence. This local process is advantageoussince it reduces the influence of the state store update on theoperation of the apparatus.

[0028] Such state storage devices are employed in particular insemiconductor memory devices.

[0029] Although the present invention has been described aboveessentially on the basis of a preferred exemplary embodiment, it is notrestricted thereto, but rather can be modified in diverse ways.

[0030] Thus, e.g. the connections 16, 25, 26, 21, 22 between theindividual apparatus units, such as, for example, the logic device 9 anda state storage device 11, 12, are not only conceivable as an electricalline but can also be realized optically.

[0031] Moreover, the invention is not restricted to the applicationpossibilities mentioned (fuse latch stores or logic circuits), butrather can be applied to any desired circuits.

LIST OF REFERENCE SYMBOLS

[0032]1 Supply voltage (Vdd)

[0033]2 Ground terminal (GND)

[0034]3 Fuse state store (fuse latch)

[0035]4 Fuse

[0036]5 First drive signal (FPUP)

[0037]6 Second drive signal (FPUN)

[0038]7 Setting of the state store (set latch)

[0039]8 Resetting of the state store (reset latch)

[0040]9 Comparison/control logic (compare/control logic)

[0041]10 Copying signal or copying instruction (copy)

[0042]11 First state storage device (e.g. first latch)

[0043]12 Second state storage device (e.g. second latch)

[0044]13 Error signal (ERROR)

[0045]14 Switching device

[0046]15 Decoding device or decoding circuit

[0047]16 Connection between first and second switching device

[0048]21 Connection between the first state storage device and the logicdevice, in particular with state signal applied to it

[0049]22 Connection between the second state storage device and thelogic device, in particular with state applied to it

[0050]23 First switching device, in particular field-effect transistor

[0051]24 Second switching device, in particular field-effect transistor

[0052]25 Connection for feeding the first drive signal

[0053]26 Connection for feeding the second drive signal

[0054] I Inverter

1. Apparatus for monitoring a state, in particular of a fuse (4),having: a first state storage device (11) for storing a state, inparticular of the fuse (4); a second state storage device (12) forstoring the state of the first state storage device (11); and a logicdevice (9) for comparing the states of the two state stores (11, 12);the first state store (11) being able to be driven for renewed readingin of the state, in particular of the fuse (4), in the event of anoncorrespondence of the states in the two stores (11, 12).
 2. Apparatusaccording to claim 1, characterized in that the first state store (11)can be driven for reading in the state, in particular of the fuse (4),by the logic device (9).
 3. The apparatus as claimed in claim 1 or 2,characterized in that the apparatus has a switching device (14), whichcan be driven by a copying signal (10) for copying the state stored inthe first storage device (11) into the second storage device (12) by thelogic device (9).
 4. Apparatus according to at least one of thepreceding claims, characterized in that the logic device (9) cangenerate an error signal (13) for indicating the noncorrespondence. 5.Apparatus according to at least one of the preceding claims,characterized in that the logic device (9) accommodates at least onesignal line (25, 26) which carries the drive signals (5, 6), inparticular, which are also fed to the first state storage device (11).6. Apparatus according to at least one of the preceding claims,characterized in that the second state store (12) is connected to one ormore decoding devices (15).
 7. Apparatus according to at least one ofthe preceding claims, characterized in that the apparatus can be used ina semiconductor memory device.
 8. Method for monitoring a state, inparticular of a fuse (4), having the steps of: storing a state, inparticular of a fuse (4), in a first state storage device (11); storingthe state of the first state storage device (11) in a second statestorage device (12); and comparing the states of the two state storagedevices (11, 12) in a logic device (9); in which case, in the event of anoncorrespondence of the states in the two storage devices (11, 12), thefirst state storage device (11) can be caused to effect renewed readingin of the state, in particular of the fuse (4).
 9. Method according toclaim 8, characterized in that the storage of the state, in particularof the fuse (4), in the first state storage device (11) is initiated bythe drive signals (5, 6).
 10. Method according to at least one of thepreceding claims, characterized in that in a manner dependent on acopying signal (10), a switching device (14) is actuated for copying astate from the first state storage device (11) into the second statestorage device (12).
 11. Method according to at least one of thepreceding claims, characterized in that in the event of a disturbanceoccurring, in particular a noncorrespondence of the states in the twostate storage devices (11, 12), an error signal (13) is generated, inparticular by the logic device (9).
 12. Method according to at least oneof the preceding claims, characterized in that the creation of a copy ofthe state from the first state storage device (11) in the second statestorage device is performed locally, in particular in a mannerrestricted to the apparatus.
 13. Method according to at least one of thepreceding claims, characterized in that it is used on semiconductormemory devices.